Fabrication and microstructure of Al2O3 matrix composites by in-situ reaction in the Al2O3-La2O3 system

Abstract

Al2O3/aluminate composites were fabricated by a solid reaction in the La2O3-Al2O3 system. The formed phase showed elongated morphology that could be controlled by varying the hot-pressing temperature and time. Dense Al2O3/LaAl11O18 composites were fabricated by hot-pressing above 1500°C. When the hot-pressing temperature was 1400°C, Al2O3/LaAlO3 composites were formed from starting composition. The grain size of monolithic alumina ceramics increased with increasing hot-pressing temperature, and marked grain growth occurred above 1600°C. However, the elongated LaAl11O18 phase suppressed the growth of alumina grains in the Al2O3/LaAl11O18 composites. Small LaAl11O18 grains existed in the alumina grains as an intragranular phase, while needlelike grains with a large aspect ratio existed at Al2O3 grain boundaries. The amount of in-situ formed LaAl11O18 phase increased with increasing amount of La2O3, and the aspect ratio of LaAl11O18 grains increased with increasing hot-pressing time.